A fructooligosaccharide (also written fructo-oligosaccharide) is a carbohydrate, which is made out of a short chain of fructose molecules. It is also classed as an oligosaccharide; oligo meaning few and saccharide, sugar. Fructooligosaccharides are also sometimes called oligofructose. Often the term is abbreviated to the letters FOS.
Together with inulin fiber, fructooligosaccharides are probably most recognized for their prebiotic qualities.
They are very similar but not identical to inulin: the difference being in their chemical structures. Fructo-oligosaccharide chains of molecules are shorter than inulin chains.